Remembering Ray Dolby – Father of Tape Noise Reduction

Though his iconic invention made him a very wealthy man, could the world of hi-fi and music be very different today if Ray Dolby hasn’t bequeathed his invention to the public for almost nothi

By: Ringo Bones   

Sadly, Ray Dolby passed away Friday, September 13, 2013 aged 80. Forever remembered after the iconic noise reduction system that bears his name, the music and hi-fi world would probably not exist as we know it today without his inventive solution in tackling the perennial problem of magnetic recording tape hiss.

Ever since the US Armed Forces introduced working samples of World War II era German analog open-reel tape recordings and their associated tape recording and playback equipment near the end of the 1940s in various trade expos, many American audio engineers suddenly got an epiphany that tape hiss or noise is not going to be an easy problem to solve. This is so because tape noise results mainly from the lack of homogeneity of the magnetic coating. Even with existing technology – then and now – the ferrous particles can never be distributed absolutely uniformly throughout the coating and the resulting aggregations of these particles create discrete magnetic fields which – during replay – manifests itself as noise e.m.f. or tape hiss at the playback head and thus amplified along with the desired audio signal. 

Luckily, a then young electronics engineer named Ray Dolby managed to formulate – i.e. engineered - a very cost effective solution that became a noise reduction system that is named after him. Thanks to Ray Dolby, the lowly cassette tape that was primarily created by Philips as an office dictation medium was raised to high fidelity status and became a very cost effective analog tape based music recording medium since the latter half of the 1970s and even displacing vinyl LP in popularity as a domestic hi-fi playback medium during the 1980s. In a sense Ray Dolby’s iconic noise reduction system virtually raised every cheap magnetic tape recording based media into audiophile status.   

In 1967, Henry Kloss heard about Ray Dolby’s noise reduction system – i.e. the Dolby A which was intended for professional studio recording noise reduction applications during the Rock N’ Roll era. It was Kloss who pushed for a consumer version of the Dolby A noise reduction system which is now known as the Dolby B, which Kloss originally saw as a boon to home/domestic open-reel tape users – and made the Philips compact cassette – which Philips originally intended as an office dictation medium – into a runaway commercial hi-fi success that virtually out-competed the better sounding vinyl LP near the end of the 1970s.

Thanks to his financial success, Ray Dolby also paved the way for various inventions and inventors to make domestic high fidelity a much more affordable hobby. Using the same Peter Scheiber patents of the old quadraphonic sound systems that expired with barely a whimper back in 1975, Dolby Laboratories managed to create Dolby Pro Logic – a surround sound system that made possible those relatively affordable surround sound capable home cinemas during the early 1980s that also made low-cost mediums like the VHS or Betamax video cassette tapes – and even cassette tapes – capable of life-like surround sound reproduction when used with a designated Dolby Pro Logic decoding box. 

Unbeknown to most of us, Ray Dolby first cut his teeth in the field of radio astronomy. In fact, his Dolby Noise Reduction System came from his earlier work in trying to extract very weak cosmic radio signals from background radiation noise mainly caused by our very own radio telecommunications traffic. 

Surround Sound From Cassette Tapes?

Even though they were relatively widely available during the late 1980s and early 1990s, why didn’t the surround sound encoded cassette tapes became more popular than they should?

By: Ringo Bones 

As someone who grew up during the heyday of “physical music media”, music lovers back then gauged the popularity of a newfangled music recording gimmick by how soon it is applied to the hard rock and heavy metal music genre. And though it is not as popular as it should have, finding cassette tapes that are Dolby Pro-Logic surround sound capable of hard rock and heavy metal live concerts during the late 1980s and early 1990s is enough for one old enough to ask why are these types of cassette tapes never became standard issue? But first, let’s discuss a brief history of surround sound. 

 When the concept of surround sound – as in quadraphonic sound – was let loose to consumers during the early 1970s, the best surround sound systems during quadraphonic’s heyday were discrete quadraphonic on four-track open reel tapes. This was by far the best delivery system for the quadraphonic sound system but these tapes were just too expensive for the average audiophiles of the day. Even though quadraphonic sound systems – i.e. 1970s era surround sound – expired with barely a whimper in 1975, it was a concept that was introduced rather too late for a more consumer friendly priced quadraphonic sound system, a matrix decoder type surround sound with logic steering that became the basis of the Dolby Pro-Logic surround sound system that eventually reintroduced the concept of surround sound for the home around the middle of the 1980s. 

Based on the same Peter Scheiber patents as the old quad systems which Dolby Laboratories added their own proprietary improvements, the Dolby Pro-Logic system managed to rekindle the consumers’ interest in of surround sound in the home during the mid 1980s because its surround sound encoding system can be seamlessly introduced – more or less – into two-track stereophonic audio already widely used in cassette tapes and the VHS and Betamax videocassettes of the time while still allowing the very same Dolby pro-logic encoded cassette tapes and videocassettes to be played on ordinary two-channel stereo systems with no loss of sound quality. The great thing about the Dolby Pro-Logic surround sound system is that it can impart relatively accurate surround sound steering data even on bandwidth restricted recording and playback media like the Philips compact cassette. 

All the analog based encode / decode surround sound systems - like Dolby Pro Logic – use a sum-and-difference matrixing system to shoehorn front and rear and the center channels into the main stereo pair. Front center, of course, was left-signal / right-signal mix, because L+R is what produces a phantom center in stereo. The rear channel was recorded out-of-phase in the front left and right channels, so that the process that recovers the signal will cancel out the other. Strictly speaking, the surround signal lagged the left stereo channel by 90 degrees of phase and led the right channel by 90 degrees, so that it was anti-phase between the stereo channels but only a symmetrical 90 degrees out-of-phase with either stereo channel.      

  

Unfortunately, when using the scheme as is, channel separation between adjacent channels is a lousy 3 dB, so a technique called logic steering was ultimately used to monitor the stereo signals, then “decide” which is the dominant channel at a given instant, and subtract the channel’s signal from the ones adjacent to it. For instance, when the left front signal is dominant, its signal is cancelled from left back and center front. When the surround channel is dominant, its signal is subtracted from the left and right fronts. Even with logic steering, there’s usually some leakage of the front left and right signals into the rear, so a small time delay is put in the surround channel to harness the ears’ tendency to localize sounds in the direction they are first heard from. 

Despite the good results obtained from Dolby Pro Logic encoded cassettes to recreate a believable surround-sound at the home even with a budget Dolby Pro Logic equipped receiver, most analog matrix encoded surround sound were eventually superseded by full-digital surround sound systems like Dolby Digital AC-3 surround sound and DTS starting in the early 1990s. As good as Dolby Pro Logic was – even in cassette form – its surround sound channels just don’t have the 20 KHz or greater bandwidth of full digital surround sound systems like Dolby Digital AC-3 and DTS.